Offline support usually gets added late, as a cache. Then two devices edit the same record, one overwrites the other, and a user loses an hour of work. That is not a caching bug, it is a missing conflict model. Write queue before cache. Reading offline is easy, writing offline is the hard part. Every mutation made while offline has to become a durable queued operation with a client generated id, a timestamp and the entity version the user was looking at. In React Native that usually means SQLite or MMKV, in Flutter Drift or Isar. The storage choice matters far less than whether the queue survives a force quit. Idempotency keys, not retries alone. A queued write will be sent more than once. Send a client generated idempotency key with every mutation and have the server store the result against that key, so a repeat arrival returns the original result instead of charging the card twice. Pick a conflict rule and write it down. Last write wins is a real strategy as long as it is chosen deliberately and the losing version stays recoverable. Problems start when nobody decided and the database just happened to behave that way. Never trust the device clock. Phone clocks drift and users change them. Order operations by a server assigned sequence or a version counter per entity, and keep the device timestamp only for display. Background sync has hard limits. iOS schedules Background App Refresh on its own terms and the user can disable it. On Android, WorkManager plus Doze means the job runs eventually, not soon. Design for a delay of hours, and use push triggered sync when the workflow genuinely needs speed. Test the states that actually break: two bars dropping mid request, a captive portal returning an HTML login page with HTTP 200, a server that accepts the write but fails to respond, and a device that was offline for a week while the schema changed. Appagentix has shipped over 110 products across more than 10 industries with a team of over 100 engineers, including HIPAA ready healthcare systems and logistics apps where sync failures have real consequences. More at https://appagentix.com and to reach the team https://appagentix.com/contact-us/